Extrusion press for hydrostatic extrusion with a billet-holding piston in the pressure chamber

ABSTRACT

In the hydrostatic extrusion of tubes using a pressure chamber and a mandrel, in order to center the mandrel the pressure chamber is divided into two parts by a piston-like billet holder, through which the mandrel passes. The billet holder includes a first portion with an opening on the mandrel and a second portion fitting within the pressure chamber. The first portion is radially slidable with respect to the second portion.

United States Patent Wrammerfors 1 Sept. 23, 1975 EXTRUSION PRESS FOR HYDROSTATIC EXTRUSION WITH A BILLET-HOLDING PISTON IN THE PRESSURE CHAMBER Inventor: Per Wrammerfors, Vasteras,

Sweden Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden Filed: Sept. 30, 1974 Appl. No.: 511,303

Foreign Application Priority Data Oct 12, 1973 Sweden 7313873 US. Cl. 72/60; 72/264 Int. Cl. BZlC 25/04 Field of Search 72/60, 264, 272

[56] References Cited UNITED STATES PATENTS Nilsson ct a]. M 72/60 Primary Examiner-Milton S. Mehr [57] ABSTRACT ln the hydrostatic extrusion of tubes using a pressure chamber and a mandrel, in order to center the mandrel the pressure chamber is divided into two parts by a piston-like billet holder, through which the mandrel passes. The billet holder includes a first portion with an opening on the mandrel and a second portion fitting within the pressure chamber. The first portion is radially slidable with respect to the second portion.

3 Claims, 2 Drawing Figures Sheet 1 of 2 r. 3 E \N Sept. 23,1975

US Patent Sheet 2 of 2 US Patent Sept. 23,1975

I 'EXTRUSION PRESS FOR HYDROSTATIC EXTRUSION WITH A BILLET-HOLDING PISTON IN THE PRESSURE CHAMBER BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to an extrusion press for the hydrostatic extrusion of tubes, and more particularly to an arrangement for centering the mandrel.

2. The Prior Art The present invention relates to a press for hydrostatic extrusion of the type having a billet holder shaped as a piston which divides the pressure chamber into two spaces and, when pressure medium is supplied to one space, achieves a difference in pressure between the two spaces when the axial movement of the piston is slowed down. When a billet is inserted, the billet and a die are placed directly in front of the opening of a movable high-pressure cylinder forming part of the pressure chamber, after which the pressure chamber is moved over the end billet, a pressure medium then being supplied to the space on'one side of the piston. The piston is then displaced towards the billet. When its movement ceases, a pressure difference arises between the two sides of the piston and an axial holding force occurs because of the pressure difference which keeps the billet and the die pressed against a die support. The inserting member can now be removed and the cylinder be further moved in over the billet and the die so that the pressure chamber is completely closed and the extrusion can be performed. Presses of this type are described more fully in US. Pat. Nos. 3,531,965 and 3,751,958.

In the extrusion of tubes, a tubular billet is the starting material and a mandrel arranged permanently in the press is used for shaping the hole in the tube. An extrusion press for commercial production is suitably horizontal. A billet-holding piston with a central opening for the mandrel makes it possible in a simple manner to center the mandrel in relation to the pressure chamber and a billet which is to be inserted into this chamber. During the extrusion, the mandrel is centered in the die opening by the material in the gap between the mandrel and the die. If the center of the die is displaced with respect to the center of the pressure chamber, detrimental stresses may occur in the mandrel if the clearance between it and the billet-holding piston is so small that a good guiding and scaling is obtained. which is important from the point of view of operations.

SUMMARY OF THE INVENTION According to the invention, the problems are eliminated by the fact that the billet-holding piston is designed so that it contains a first inner portion with an opening suitably adjusted to the mandrel and a second outer portion with an outer diameter suitably adjusted to the inner diameter of the pressure chamber said portions being arranged so as to be radially displaceable with respect to each other. The first inner portion suitably consists of a bushing inserted in the billet holder. The billet holder should contain resilient ele ments which tend to center the mandrel and, accordingly, to position the mandrel in relation to the billet holder and the pressure chamber. This will make it possible to design the billet holder so that a satisfactory scaling is obtained between the billet holder and the mandrel and the wall, respectively, as well as a satisfactory guiding of the mandrel.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described more fully with reference to the accompanying figures.

FIG. I shows a pressure chamber in a press for hydrostatic extrusion according to the invention and FIG. 2 shows in more detail the billet holder and the die and the pressure chamber parts around them.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, 1 designates a pressure chamber formed of a high-pressure cylinder 2, a pressuregenerating punch 3 and a die 4 resting on a die support 5. The cylinder 2 may be built up of an inner tube 6 (liner) which is surrounded by an outer tube 7, possibly a prestressed strip sheath, and end pieces 8 and 9. These end pieces act as supports for seals 10 and I I between which there is a spacing tube I2. Inside the highpressure cylinder is a unit 13 consisting of a spacing tube 14, an mandrel 15, a plate 16 transmitting forces from the mandrel to the spacing tube 14, a lid 17 and springs 58 fixing the mandrel in the plate 16 and a billet holder 18 axially movable within the tube I4 and along the mandrel 15, which centers the mandrel 15. During the extrusion the mandrel force is transferred by way of the plate 16 and the tube 14 to the die 4. During the other stages of a work cycle the unit 18 is axially fixed by the locking rings 19 and 20 in the tube 12. There is a certain axial clearance. Through the lid 17 and the plate 16 there is a channel 21.

The billet holder 18 divides the pressure chamber I into two spaces 22a. 22b and 23. The space between the pressure-generating punch 3 and the billet holder 18 is divided into two sections 22a and 22b by the plate 16. In the space 23 between the billet holder 18 and the die 4 there is a billet 27. The billet holder contains a portion 28 with two annular ridges 29 and 30 which make contact with the end surface of the billet 27 in a sealing manner and separate a space 31 from the gaps 32 and 33 between the billet 27 and the tube 14 and the mandrel 15, respectively. The billet holder is thus provided with means for connecting it to the billet. The billet holder is also provided with a guide 34 having ribs 35 for centering the billet 27 and provided with grooves 36. In the billet holder 18 there is a forward flow path for pressure medium, consisting of the channel 37, the valve housing 38 with a valve member 39 and a valve spring 40, and the channels 41 and 42. Upon a pressure difference between the two sides of the billet holder determined by the valve member 39, this flow path allows pressure medium to flow from the space 22b to the gaps 32 and 33. There is also a return flow path consisting of the channels 45 and 46, the valve housing 47 with the valve member 48 and the spring 49, and the channel 50, said flow path permitting pressure medium to flow in the opposite direction when the volumes of the gaps decrease during the extrusion process. In the billet holder portion 28 there is a bore hole 51 in which there is arranged a bushing 52 which is axially fixed by a locking ring 53. Between the hole 51 and the bushing 52 there is a clearance so that the bushing 52 is able to move radially in relation to the billet holder portion 28.

The billet holder 18 according to FIG. 2 comprises a front guiding portion 60, an intermediate portion 61 with a valve housing 65 with a valve member 62, which is pressed against a seat in a lid 63 by a spring 64, with a valve housing 66, with a check valve member 67 and with a bore hole 68 in which a bushing 69 having smaller outer diameter than the hole 68 is arranged. The bushing is locked in the bore hole by the lid 63. The bushing 69 is able to move radially in the bore hole and the play is chosen so that possibilty of any necessary radial movement of the mandrel is obtained. In the gap between the bore hole 68 and the bushing 69 there are centering resilient elements 70 which keep the bushing 69 and thus the mandrel when the mandrel is not subjected to radial forces. Instead of the spring elements shown in the gap. there can be used substantially sunk spring packets in the portion 6I. In the embodiment according to FIG. 2, the forward flow path will be formed by the channel 71, the valve housing 65, the channels 72, the space 73 and the channel 74, and the return flow path will be formed by the channel 74, the gap 75, the space 73, the channel 76, the valve housing 66 and the channel 77. The seals 78 and 79 prevent pressure medium from passing between the billet holder 18 and the tube I4 and the mandrel l5, respectively. It is possible to arrange the bushing 69 so as to be axially movable in the bore hole 68 in such a way that it forms a valve member in the return flow path. thus replacing the valve member 67.

I claim:

1. Press for hydrostatic extrusion of tubes comprising a-press stand. a pressure chamber comprising a high pressure cylinder displaceably arranged in the press stand, a die sealing one opening of the cylinder, said die having an opening for forming a profile. and a punch insertable in the other opening of the cylinder for generating a pressure within a pressure medium enclosed in the pressure chamber and surrounding a billet for extrusion of the billet, a mandrel arranged in the pressure chamber. a piston-like billet holder dividing the pressure chamber into two spaces and having an opening for the mandrel. said piston holding the billet and the die pressed against a die support while the pressure chamber is being closed, the billet-holding piston including a first portion having an opening adjusted to the mandrel and a second portion having an outer diameter fitting within the pressure chamber, the second portion having a bore therein of an internal diameter greater than the external diameter of the first portion, whereby the first portion is radially displaeeable in relation to the second portion.

2. Press according to claim 1, in which the said first portion comprises a bushing inserted in the billet holder.

3. Press according to claim 2, in which the billet holder contains resilient elements which tend to center the bushing in relation to the billet holder. 

1. Press for hydrostatic extrusion of tubes comprising a press stand, a pressure chamber comprising a high-pressure cylinder displaceably arranged in the press stand, a die sealing one opening of the cylinder, said die having an opening for forming a profile, and a punch insertable in the other opening of the cylinder for generating a pressure within a pressure medium enclosed in the pressure chamber and surrounding a billet for extrusion of the billet, a mandrel arranged in the pressure chamber, a piston-like billet holder dividing the pressure chamber into two spaces and having an opening for the mandrel, said piston holding the billet and the die pressed against a die support while the pressure chamber is being closed, the billetholding piston including a first portion having an opening adjusted to the mandrel and a second portion having an outer diameter fitting within the pressure chamber, the second portion having a bore therein of an internal diameter greater than the external diameter of the first portion, whereby the first portion is radially displaceable in relation to the second portion.
 2. Press according to claim 1, in which the said first portion comprises a bushing inserted in the billet holder.
 3. Press according to claim 2, in which the billet holder contains resilient elements which tend to center the bushing in relation to the billet holder. 